Northstar Engines and System Technical Discussion Discussion, WOT - is this the ONLY way to remove carbon buildup? in Cadillac Engine Discussion; So do you shift into 2nd while you're going 55mph, or start in 2nd from a stop? I just want ...

Re: WOT - is this the ONLY way to remove carbon buildup?

Get a spray bottle and fill it with plain tap water. Get the engine started and up to about 2000RPM. With the air filter out spray the water into the intake and watch the carbon come out the exhaust. Knowledgeable mechanics have been using this procedure for at least 100 years.

Re: WOT - is this the ONLY way to remove carbon buildup?

So do you shift into 2nd while you're going 55mph, or start in 2nd from a stop? I just want to be sure I do this correctly.

Accept the fact that the engine and transmission controls will NOT let you break anything .................read the service manual on transmission controls protocol.

If your car is in otherwise good mechanical condition .......... Find a clear, deserted stretch of highway/open road. Pull to the shoulder and place the stick in 2 (This action says "This is my preferred gear"). Traffic all clear ??? Ease onto the road and, from a slow rolling start, stick the gas pedal through the firewall and leave it there.The car will accelerate in 1st and at redline it will shift to 2nd and continue to accelerate. Just before the 2nd gear redline - ~6300 rpm - flip your foot off the gas pedal and allow the engine to brake the car down to < 20 mph. The transmission will downshift as necessary to keep the engine rpm in the proper band. Miss the 2nd gear redline and upshift ?....... Coastdown and do it again. Lots of smoke and crap out the tailpipe first time ?? Do it again......... You'll get to about 80 mph or so at the foot-off-the-gas point.

Why did we put the stick in 2 ???? Because that forces the downshift at high rpm coastdown: The theory behind the "WOT" is to load and heat the pistons and rings to the max during forced acceleration - then radically unload them with high vacuum during the coastdown. This load-heat-unload-cooldown chips away carbon flakes and allows the piston rings to work in their grooves, further shedding carbon buildup.

Where does some carbon buildup come from ??? Granny, grandpa and city driving. Gears - the 4T80E will always protect itself and the engine - neither allowing an over-rev or excessively high rpm downshift. You can, if you have the track room, take the car to speed limiter cutoff with the stick in 1st - upshifts will occur ONLY at full load redlines. I know for an absolute fact that my STS will do at least 143 with the stick in 1 - that's also just above where the 3 - 4 redline shift occurs. Yes, these cars (VIN 9) will do over 130 in 3rd.

......... and that procedure explained by dkozloski is an old, time-honored method of cleaning piston tops......... DO NOT spray any solid water - mist only, and know that the procedure is not as effective in a throttlebody-long runner-center log intake manifold system as it is in a down-the-throat carburetor system. Large reciprocating aircraft engines have used water injection for high power application demands for a very, very long time.......... it slows down the combustion process and keeps max combustion pressure in the cylinder for more rotation duration - as well as cleaning the piston tops.

Of course, we could always read back through the entire thread - and post #9 - to get further insight ........... and, in answer to the original thread title, there's a sticky just above this thread which talks about the GM ring cleaning procedure using potent chemicals.

Re: WOT - is this the ONLY way to remove carbon buildup?

Thanks for the detailed explanation for this newbie. I'll be sure and do this procedure ASAP and see what results I get. I cannot imagine doing 143 in this car! WOW! Mine is a VIN letter Y instead of a 9, but I assume the process is the same either way. Thanks again for the assistance.

Re: WOT - is this the ONLY way to remove carbon buildup?

Well, I took my Deville out on the interstate earlier today and gave it three good WOT runs. Now I'm not entirely sure I did it altogether correctly, but I did not get any smoke from the exhaust whatsoever. My conclusion is, I either didn't perform the runs correctly, or my engine is in good shape and quite clean. I started in 2nd gear from a dead stop and floored it I watched the rpm's but each time the transmission up-shifted, they would drop and then climb again. When I saw the rpm's around 6300 or so and my speed was up around 97, I let off the accelerator entirely and waited for the car to slow on it's own back to around 55mph. Somewhere during the slow down (not sure what speed or rpm) there was a stout drop in rpm and speed and I could feel the engine brake the car with a fairly strong jerk and then the speed and rpm's dropped rapidly back down to 55mph. As soon as I hit 55, I floored it again (all the while in 2nd gear) and repeated the run three times in a row. I never did see any smoke from the exhaust. Now, if it sounds to any of you experts like I did something wrong here, please correct me and be as specific as possible, because I am new to all of this and I want to learn how to do this properly. I am sincerely hoping to give my Deville the proper care & maintenance and avoid any of the horror stories I have heard about head gaskets & head bolts, even though that's not related to the WOT procedure. Thanks for all the advice & help you've given me thus far. I really appreciate it!

Re: WOT - is this the ONLY way to remove carbon buildup?

You done good.

EDIT: The stick might have been in 2 (correctly) but the transmission will always upshift at redline and downshift at a speed that will not over-rev the engine in the next lower gear. The shift(s) and downshift you experienced are perfectly normal for that situation.

Re: WOT - is this the ONLY way to remove carbon buildup?

Sounds to me like you did it correctly. Just keep in mind that you do not need to go that fast. If you can do it safely, that's fine, otherwise 75-80 will suffice. It's not worth a ticket or an accident.

Re: WOT - is this the ONLY way to remove carbon buildup?

Originally Posted by maeng9981

Of all the WOTs I gave to my cars, I could never see any smoke from my own rear end, but others have told me that they've seen the carbon cloud.

That's because you were looking the proper way, down the road instead of looking back. (joking). I have seen a little cloud a few times. Perhaps the higher RPM in the L37 results in more of the smoke release vs. the LD8? probably not. It is difficult to see the smoke unless it's at night and there's a car behind you. If there is a lot of space behind you or if there are no cars, you would need something there to provide visual contrast in order to see the light gray smoke.